Écrans bénévole et référent redessinés, messages aux bénévoles

Étape 55 : écrans /mobile-benevole et /mobile-referent d'après la maquette
(design/Planning bénévole mobile) — créneau en cours ou prochain mis en
avant, planning par journée de festival avec frise horaire, compteurs et
pointage du référent par créneau.

Étape 56 : message de l'organisation (Edition.volunteer_message, onglet
« Message aux bénévoles ») et message de chaque poste (Position.message,
saisi par le référent), migration 0029, affichés sur l'écran bénévole.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/api/mock/mock-client.ts

@@ -44,6 +44,7 @@ import type {
   VolunteerRead,
   EditionStats,
 } from '../schema';
+import { MESSAGE_MAX_LENGTH } from '../schema';
 import { getAuthToken } from '../session';
 import { ApiError, type PlanningApi } from '../types';
 import { buildMockState, type MockPendingSubmission, type MockState } from './dataset';
@@ -836,6 +837,14 @@ function runSolver(): SolverRunResult {
   };
 }
 
+/** Message (organisation, poste) comme l'API : bords retirés, vide = plus
+ * de message, 2000 caractères au plus. */
+function checkMessage(value: string | null | undefined): string | null {
+  const text = (value ?? '').trim() || null;
+  if (text && text.length > MESSAGE_MAX_LENGTH) throw new ApiError(422, 'error.generic');
+  return text;
+}
+
 export function createMockApi(): PlanningApi {
   return {
     editions: {
@@ -847,6 +856,13 @@ export function createMockApi(): PlanningApi {
         if (body.start_date) next.start_date = body.start_date;
         if (body.end_date) next.end_date = body.end_date;
         if ('retention_days' in body) next.retention_days = body.retention_days ?? null;
+        if ('volunteer_message' in body) {
+          const text = checkMessage(body.volunteer_message);
+          if (text !== next.volunteer_message) {
+            next.volunteer_message = text;
+            next.volunteer_message_updated_at = text ? touch() : null;
+          }
+        }
         if (next.end_date < next.start_date) {
           throw new ApiError(422, 'edition.dates_inconsistent');
         }
@@ -1124,6 +1140,8 @@ export function createMockApi(): PlanningApi {
               position_location: position?.location ?? null,
               referent_name: referent ? `${referent.first_name} ${referent.last_name}` : null,
               referent_phone: referent?.phone ?? null,
+              position_message: position?.message ?? null,
+              position_message_updated_at: position?.message_updated_at ?? null,
             };
           })
           .sort((a, b) => a.starts_at.localeCompare(b.starts_at));
@@ -1384,6 +1402,8 @@ export function createMockApi(): PlanningApi {
           location: body.location ?? null,
           category: body.category,
           lead_account_id: body.lead_account_id ?? null,
+          message: null,
+          message_updated_at: null,
           created_at: now,
           updated_at: now,
         };
@@ -1395,6 +1415,13 @@ export function createMockApi(): PlanningApi {
       update: (_edition, id, body) => {
         const p = state.positions.find((x) => x.id === id) ?? notFound();
         if ('lead_account_id' in body) checkLeadAccount(body.lead_account_id);
+        if ('message' in body) {
+          const text = checkMessage(body.message);
+          if (text !== p.message) {
+            p.message = text;
+            p.message_updated_at = text ? touch() : null;
+          }
+        }
         Object.assign(p, {
           ...('name' in body ? { name: body.name } : {}),
           ...('location' in body ? { location: body.location ?? null } : {}),